Up to 10,000 people could have been affected by the scandal where they opted out of their tracker deal for a while when European Central Bank rates rose. Often, they had been assured by their bank that they could return to the tracker, but were denied this option.

Now many of these people could be getting their trackers restored, have interest overpayments repaid, and get compensation for the overcharging.

A tracker has an interest rate set at the prevailing European Central Bank (ECB) lending rate, which is zero at present, plus a margin which is usually 1pc. And the ECB main lending rate is set to stay low for years.

This means a typical tracker mortgage holder is paying 1pc at the moment, compared with close to 4pc on a variable rate.

The gulf between those on trackers and those on standard variable rates is now as high as 3pc - a gap which will see a person with a €300,000 variable rate mortgage paying more than €400 a month, or almost €5,000 a year more on loan repayments than someone with a tracker the same size.

The Central Bank is currently conducting a probe across all banks over the wrongful removal of trackers from families.

The final number of families affected could be as high as 10,000, according to financial adviser Padraic Kissane, who specialises in tracker restoration cases.

But it will be 2017 before the industry-wide probe is completed, the Central Bank said. Banks have now set out their plans for dealing with the investigation.

The banks' plans for dealing with the tracker-loss cases is are now being reviewed by regulators.

"The scale and complexity of this examination means that this work will be ongoing through 2016 and will conclude in 2017," the statement said.

Banks have been told by regulators to move to the next phase of the investigation and identify any customers impacted by their failure to restore them to trackers.

And it emerged recently that the Central Bank is not satisfied with the responses it is getting from Ulster Bank on the tracker removal issue.

This has prompted Central Bank to consider taking enforcement action against the bank.

This is the second bank to face an enforcement action from regulators over the issue, following the move against Permanent TSB.

Last summer Permanent TSB conceded that it has to restore almost 1,400 people to trackers and to compensate them.

These people lost trackers when they opted for a fixed rate when the main ECB rate began to rise in 2007 and 2008.

The homeowners exited the fixed rates early - before the term was up - and expected to revert back to the tracker, but were denied this option by their bank.

The Central Bank action against Ulster Bank is separate to the all-bank review of tracker-loss cases the Central Bank has asked lenders to conduct.

The enforcement action is understood to involve those who took out tracker mortgages with First Active, which was taken over by Ulster Bank in 2009, along with Ulster Bank trackers.

The Central Bank has the power to administer sanctions for contraventions by regulated firms and ban managers if it finds there have been failings. Fines of up to €10m can be imposed.

All this means it could still take a while, but those who wrongly lost a tracker could soon have something to celebrate.